Field of the Invention
The invention relates to a circuit configuration for smoothing an input voltage applied to two input terminals, with the aid of a low-pass filter and a negative-feedback amplifier having one input connected to a capacitor and an output connected to an output terminal.
One such circuit configuration for smoothing an input voltage is known, for instance, from the book by U. Tietze and C. Schenk, entitled: Halbleiter-Schaltungstechnik Semiconductor Circuit Technology!, Springer-Verlag, 7th Edition, 1988, p. 400. In that circuit, an RC element including a resistor and a capacitor is provided as the low-pass filter and is followed by a negative-feedback amplifier as an impedance converter. An output of the impedance converter is applied to an output terminal and, through an ohmic voltage divider, to the reference potential. The voltage tap of the voltage divider is coupled to the inverting input of the operational amplifier. The known circuit makes largely load-independent properties of the low-pass filter possible as well as a free choice of the direct voltage gain.
Particularly in an integrated circuit configuration, the known smoothing circuit has the disadvantage of only permitting very small time constants to be achieved.
Both the resistor and the capacitor require a large area on a chip, and that results in high chip costs. An external RC low-pass filter, on the other hand, requires elements with high electric strength and entails additional expense for connection pins.